The present invention relates to a gas separation membrane comprising at least one thin film mainly containing at least one particular aromatic polyimide or copolyimide, preferably prepared from at least one tetra-ester or diacid-diester derived from 3,3',4,4'-tetracarboxylic acid.
The use of aromatic polyimides in gaseous permeation membranes has been notably described in U.S. Pat. Nos. 4,378,324, 4,378,400, 4,512,893, 4,705,540, 4,717,393, 4,717,394 and 4,718,921.
None of these patents mentions the use of 3,3',4,4'-tetracarboxylic benzhydrol acid derivatives for preparing polyimides that can be utilized for gas separation.